查看更多>>摘要：Slender footbridges are prone to excessive vibrations due to pedestrian effects,and comfort criteria often govern their design. In this sense, composite materialsthat combine high damping capacity with relatively high stiffness andlow mass can provide functional benefits. This paper presents a study of thedynamic behaviour of an 11 m long hybrid footbridge made of two I-shapedpultruded glass fibre reinforced polymer (GFRP) main girders and a thin steelfibre reinforced self-compacting concrete (SFRSCC) deck, in operation since2015. The main goals were (i) to improve the knowledge of the dynamic propertiesof composite footbridges and (ii) to assess the benefits of using a structuremade of pultruded GFRP instead of a conventional material (steel),namely, considering its greater ability to dissipate energy. The resonant frequencies,damping ratios, and mode shapes of the footbridge were identifiedbased on experimental testing. A finite element (FE) model of the footbridgewas developed and calibrated with test data and used to simulate the effects ofpedestrian loads. Simulations of the same type were conducted on an equivalentstructural system made of steel profiles. The simulation results of the twoshort-span footbridges with similar natural frequencies enhance the impact ofhigh-order harmonics of the pedestrian load in the dynamic response. It is alsoshown that polymer-based components can contribute to limiting vibrations infootbridges or even act as self-dampers.
查看更多>>摘要：The contribution of masonry infill walls (MIW) to the dynamic behavior ofreinforced concrete (RC) buildings is investigated in this study. An existingnon-symmetrical, six-story reinforced concrete building has been used as a testspecimen. Dynamic characteristics of the building have been determined bythe ambient vibration survey (AVS) first. Then, the masonry infill walls on itsground floor were completely demolished, and the obtained new form of thebuilding was studied by AVS. Later on, two forms of the building weremodeled to visualize its behavior under ambient conditions, and the dynamiccharacteristics of the building have been determined numerically. The attainedexperimental and numerical results for both forms of the building were compared,and the constructed numerical models of the building were calibratedby an interactive tuning algorithm defined according to the specific dynamicfeatures of the building. As the last numerical analysis, all MIW were removedfrom the verified numerical model of the building and the dynamic analysiswas repeated. The main goal of the study was accomplished by comparing theexperimentally and numerically obtained dynamic results on the basis of dominantfrequencies, mode shapes, torsional behavior, and soft story mechanism.
查看更多>>摘要：The mitigation of bridge cable vibration has long been a research hotspot withsubstantial developments contributed to the field. In addition to vibration control,a recent development trend incorporates auxiliary sensors, local computingmodules, and data transmission devices to establish a comprehensive,integrated cable control and health monitoring system, which requires externalenergy input. However, an external power supply for these devices is notconsidered an attractive option, considering that the kinetic energy embodiedin cable vibrations can be potentially harvested to cover such power demand,leading to the establishment of an independent self-powered control andhealth monitoring system. In this regard, we proposed an unprecedentedsolution for cable vibration mitigation by developing a novel H-bridge-basedelectromagnetic inerter damper (HB-EMID) in this work, in which HB-EMIDcan emulate the control behavior of an inerter damper and possess an energyharvestingfunction. Meanwhile, the newly proposed HB-EMID is granted withgreat flexibility that can alter its equivalent mechanical properties by merelyadjusting the corresponding coding. Following the introduction of the systemtopology and working mechanism, this study applies an HB-EMID to a cablestructure and systematically investigates the balanced control and energyharvestingperformances, as well as its feasibility to full-scale application. Bothsatisfactory control performance and sufficient harvested power are confirmedthrough numerical validation.
查看更多>>摘要：For precisely disclosing the seismic performance of tuned liquid damper (TLD)vibration control structures, the shaking table substructure test (STST) methodis presented and experimentally validated, and the parametric effects on thereduction efficiency of TLD are further investigated by using the STST methodin this paper. Firstly, one optimal design method of TLD for high-rise structuresis presented. Secondly, the STST based on three variable control method(TVCM) for the TLD vibration control structures is presented. Thirdly, theeffectiveness and robustness of the STST for TLD vibration control structuresare validated by a series of tests on one three-story-frame structure with a rectangularTLD. Finally, the parametric effects on the reduction efficiency ofTLD, in terms of mass ratio and liquid depth, are investigated using the STSTmethod. Experimental results show that the displacement and accelerationresponses of the STST match well with that of the traditional shaking tabletests under El Centro (NS, 1940) and Taft earthquake wave record excitations,which indicates the effectiveness and the robustness of the STST based onTVCM for TLD vibration control structures. It is also shown from the experimentalresults that the best mass ratio and liquid depth are 4% and 40 mm,respectively, which are consistent with the optimal designs of TLD. Moreover,the control performance of TLD is not only related to its parameters but alsorelated to the spectral characteristics of ground motion excitations.
查看更多>>摘要：Estimating the load distribution of a bridge structure enables to evaluate thein-service state and predict the structural responses. This paper develops aniterative strategy to inversely estimate the traffic load distribution of a bridgefrom limited measurements. The computer vision technologies, including theYOLO network-based object detection and a pixel coordinate-based positioningapproach, are used to locate the vehicle positions on the bridge deck and forma prior information vector of the input positions. Then, a generalized Tikhonovregularization method is proposed to estimate the load distribution using thebridge response and prior information. The regularization parameter is determinedby the L-curve method. The fusion of computer vision and regularizationcan improve the load identification accuracy and reduce the overfittingeffect. The developed approach is applied to numerical and experimentalexamples under various load conditions. The load can be accurately identifiedin all cases, and the full-field responses of the structures can be reconstructedwith minor errors.
查看更多>>摘要：Embedded strain sensors are the primary measurement device for strain in thetensile layer of asphalt pavement. The favorable deformation compatibilitybetween embedded strain sensor and asphalt layer is the key to ensure the precisemeasurement of mechanical response. However, the good deformationcoordination may be difficult to maintain under different environments due tothe viscoelasticity of asphalt mixture. In this study, 4-point bending beam testswere performed to investigate deformation compatibility between embeddedstrain sensor and asphalt mixture under different temperature. Then, a quasistaticfinite element model (FEM) was employed to simulate static mechanicalresponse of asphalt pavement, and the design requirements for embeddedstrain sensor were proposed considering deformation coordination. In addition,the rationality of the design requirements of the sensor was further validatedin the dynamic response monitoring. The results indicate that thedeformation compatibility between embedded strain sensor and pavementmaterial changes at different temperatures. In order to ensure favorable deformationcompatibility, the reinforcement of the protective housing should beeliminated and the equivalent modulus (EM) of the sensitive element shall bethe same as that of the asphalt mixture. Considering the viscoelasticity ofasphalt mixture, the strain sensor with lower EM is recommended in thedynamic response monitoring of pavement structure. This study provides abasis for optimizing the embedded strain sensor of asphalt pavement from theperspective of deformation compatibility.
查看更多>>摘要：To improve the applicability of mass dampers in control problems facing differenttypes of uncertainties, asymmetric nonlinear energy sink-inerters(ANESIs) are proposed. Previous studies reveal that ANESIs have excellentcontrol effect in mitigating impulsive responses but only briefly touch upontheir seismic application. This study is intended to provide better understandingin this regard by analyzing the dynamics of the ANESI system when subjectedto harmonic and seismic ground excitations. First, the development ofANESIs is described and the theoretical model of ANESIs is updated in accordancewith the experimental validation on a three-story steel-frame structure.Then analytical investigations are carried out and subsequently a designmethod is proposed for the ANESI system when subjected to harmonic groundexcitation. Finally, 12 seismic ground motions are applied to the ANESI systemto assess its control effectiveness, energy and frequency robustness, and spacedemand. The results show that devices with inerter are in general more effectivethan those without inerter and the ANESI outperforms its linear andnonlinear counterparts with stronger robustness against changes in structuralproperty and energy level, demonstrating great potential in seismicapplication.
查看更多>>摘要：Estimating modal parameters requires significant user interaction, especiallywhen parametric system identification methods are used and the physicalmodes are selected in the stabilization diagram. In this paper, a fast densitypeaks clustering algorithm combined with the covariance-driven stochasticsubspace identification method is used to automatically identify modal parameters.Before the automatic identification process, the spurious modes from thestochastic subspace identification method were eliminated by a two-stagemethod, including using the soft and hard verification criteria to remove spuriousmodes in the first stage and the removal of spurious modes based on thestability of physical modes in the second stage; thus, a better stabilization diagramwas obtained for the subsequent automatic identification. Furthermore,fast density peaks clustering algorithm was applied to select the appropriatestructure modes from the stabilization diagram. In the entire identificationprocess, no user participation was required. The proposed method was demonstratedon a 4-degree of freedom (DOF) numerical model and a benchmarkframe structure, and the results indicated that the modal parameters can beidentified accurately even with the noise effects using the default user-definedparameters. This method showed higher efficiency and universality than theexisting methods. Finally, the applicability and robustness of the proposedmethod in automated operational mode tracking were verified on a real cablestayedbridge.
查看更多>>摘要：System identification is primarily studied for unidirectional excitation usingthe Bouc-Wen model, neglecting the torsional coupling, even though realstructure experiences multidirectional seismic excitation. Moreover, the highdamping rubber bearings exhibit bidirectional effects, thereby requiringcoupled biaxial Bouc-Wen (BBW) model and demand the estimation of modelparameters for structural health monitoring. The current work presents threenumerical case studies followed by experimental validation to demonstrate theapplicability and efficacy of Bayesian filters named constraint unscentedKalman filter (CUKF) in identifying model parameters for the nondeterioratingsystem as well as deteriorating systems. With limited measurementsand increased states, a two-stage framework of the CUKF is used toenhance the performance in identifying the hysteresis parameters and systemdynamics of the nondeteriorating systems. For the deteriorating system, theParis-Erdogan law is coupled with the stiffness in the BBW model to introducedegradation as per the acceleration fatigue crack growth. The degradationparameters and deteriorating stiffness is captured through CUKF accurately.The application of CUKF to the experimental responses proves the robustnessof the algorithm for coupled biaxial hysteresis system. Additionally, a unifiedstructural health monitoring (SHM) framework is proposed for condition monitoringduring extreme events and long-term periodic maintenance throughambient vibrations. Overall, the result concludes that CUKF is a reliableBayesian estimator for coupled biaxial hysteresis systems and demonstratespromising potential in identifying fatigue-induced deterioration.
查看更多>>摘要：To improve the resilient capability of bridges, a novel multi-stage superelasticvariable stiffness pendulum isolator (SVSPI) is developed by incorporatingsuperelastic shape memory alloy (SMA) with the multi-stage variable stiffnesspendulum isolator (VSPI), which featured with the favorable adaptabilityunder service conditions and near-fault excitations. Based on OpenSees platform,the numerical model for novel multi-stage superelastic variable stiffnesspendulum isolator is created. A fractional factor based design method issuggested for parameter optimization of the multi-stage superelastic variablestiffness pendulum isolator. The example bridges with the novel isolators aredesigned to conduct the seismic mitigation investigation under near-faultearthquakes. The effectiveness of the novel superelastic multi-stage variablestiffness pendulum isolator and suggested design method is further discussedby case study. Results show that the novel multi-stage superelastic variablestiffness pendulum isolator designed by the proposed fractional factor baseddesign method can perform the dual control of the isolator residual displacement,girder displacement, and base forces in piers for bridges. The effectivenessof the multi-stage superelastic variable stiffness pendulum isolator withthe optimal parameters is demonstrated by case study. The technical achievementscan provide reliable basis for structural resilience enhancement andpotential structural applications.
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Wiley